Catalytic treatment in stainless steel apparatus



Patented Jan. 13, 1942 UNITED STATES. PATENT OFFICE,

CATALYTIC TREATMENT IN STAINLESS STEEL APPARATUS Robert P. Russell, Millburn, N. J., assignor to Standard Oil Development Company, a cornotation of Delaware No Drawing. Application August 19, 1939,

- Serial No. 291,041.

2 Claims.

This invention relates to iron alloys of the type known as 25-20 stainless steel, and is more particularly concerned with an improved alloy of this type which is especially resistant to attack by carbon oxides.

Stainless steels of the 25-20 type contain from 24 to 26% chromiiun, 19 to 21% nickel and the balance iron and small amounts, usually less than 1%, of silicon, phosphorus, manganese and carbon. These steels are used extensively in processes for treating hydrocarbon oils at high temperatures and in the presence of hydrogen or other gases. Processes of this type are cracking, reforming, catalytic cracking, catalytic reforming and catalytic reforming in the presence of hydrogen.

In catalyticcracking a hydrocarbon oil such as a gas oil is. passed-at a. temperature of 700 to 850 F. and under atmospheric or slightly elevated pressure over a catalyst such as Super-Filtrol,

natural or activated clays of the bentonitic or' montmorillonitic type, aluminum silicate, silica gel and the like, for the purpose of producing motor fuel, of increased octane number.

p In catalytic reforminga hydrocarbon oil consisting essentially of hydrocarbons boiling'substantially in th gasoline range is passed at a temperature between 850 and 1050 F. under atmospheric or slightly elevated pressure and at a rate between 0.3 and 5.0 volumes of liquid oil per volume of catalyst per hour over a catalyst comprising a carrier or support such as alumina,

silica gel, etc. and an active oxide of 'ametal of the IV, V, VI or VIII groups of the periodicsystem, for the principal purpose of increasing In all these catalytic processes the activity of the catalyst for promoting the reactions desired is gradually destroyed because of the deposition or formation on the catalyst of carbonaceous contaminants such as coke. It is then necessary to regenerate the activity of the catalyst and this is usually done by passing a mixture of hot inert gases and regulated quantities of air or oxygen therethrough whereby the coke and carbonaceous materials are removed by combustion. The flow of gases'is ordinarily continued until no more oxygen is consumed. This indicates that most if not all of the coke has been burned oflf. The'length of time that the catalyst can be used before requiring regeneration will depend upon how long the product produced meets the desired specifications. This time will vary from as little as seconds in the caseof catalytic cracking to as long as 6 to '12 hours or more in the case of catalytic reforming in the presence of hydrogen. It is of course desirable to be able to use the catalyst as long as possible before it requires regeneration and it has been found that by conducting the catalytic process in the presence of substantial quantities of added or recirculated hydrogen the tendency for coke deposition on the catalyst is greatly retarded and at the same time the quality of the product is still further increased;

30 During the regeneration of the catalysts used in these processes the coke is removed by combustion. Thus large quantities of carbon monoxide and carbon-dioxide are formed. The temperatures'during regeneration are ordinarily between 650 and 900"- F. but spot temperatures as the octane number of the hydrocarbon oil without causing extensive reduction in molecular weight or boiling point. Among the reactions which occur in catalytic reforming to a greater or lesser extent depending upon the character of the feed, the .type of catalyst and the operating conditions are dehydrogenation, aromatization or cyclization, desulfurization, isomerization and alkylation.

In catalytic reforming in the presence of hydrogen a hydrocarbon oil comprising hydrocarbons boiling substantially in the gasoline range high as 1200, F. may be encountered. Under these conditions, definite though relatively minute quantities of iron carbonyl are formed by interaction of the iron in the steel'parts of the 40 apparatus and the carbon oxide evolved in the is passed over a catalyst together with substantial quantities of hydrogen or a gas rich in free hydrogen at a temperature between 850 and 1050 F., under a pressure between 50 and 500 lbs. per

square inch,and' at a rate between 0.3 and 5.0 volumes of liquid oil per volume of catalyst per hour. The reason for using hydrogen will be apparent from what follows:

combustion.

Nearly all catalysts used these catalytic processes are sensitive to and poisoned by mithereon.

I have found that by incorporating small quantitles of silver in the 25-20 stainless steel used for the construction of reactors and tubing for catalytic processes of the type described, the tendency for the formation of iron carbonyl or at any rate for the deposition of minute traces of iron on the catalyst is substantially retarded or altogether prevented.

The quantity of silver added to the stainless steel alloy is in general below about 2%, and in most cases from 0.20 to 1.80% silver is suflicient. Thus a typical alloy would have a composition of 24% chromium, 19% nickel, 1.2% silver, and the balance iron and small amounts of carbon, silicon, phosphorus and manganese which do not interfere with the efiect of the silver on the steel.

This silver containing stainless steel may be usedfor the construction of the entire apparatus or it may be useed merely for the lining of thos parts of the apparatus which come into contact with hot gases containing carbon monox ide; Ordinarily the reaction vessels used for catalytic processes of the type described have an inner lining of the 25-20 stainless steel and the outside is constructed of ordinary steel. In these cases the inner lining only need be made of the silver containing steel.

By using these silver alloys in catalytic reforming in the presence of hydrogen in place of the .25-20 stainless steel without the silver I have found that the activity of catalysts comprising activated alumina and chromium oxide or molybdenum oxide can be brought back by regeneration to substantially the initial activity of the fresh catalyst. In nearly every case previously it has been observed that after even the flrst regeneration the catalyst is not restored to its original activity and after each regeneration the activity is brought back to a progressively lower level. -When using .the silver 25-20 stainless steel alloy I have found that this progressive decrease in post-regeneration activity is greatly retarded. It will be understood that while this silver alloy has been described as being. of particular value in catalytic processes for treating hydrocarbon oils, it is of equal value in any process in which the formation of iron carbonyl and its subsequent decomposition may have deleterious efiects.

This invention is not limited by any theories of the mechanism of the reactions nor by any details which have-been given merely for purposes of illustration but is limited only in and by the following claims in which it is intended to claim all novelty inherent in the invention.

I claim:

1. In the catalytic treatment of hydrocarbon oils in apparatus constructed of the 25 chromium-20 nickel type stainless steel and in the presence of a catalyst which requires periodic regeneration to restore its activity, said regeneration being effected by burning off the coke deposited on the catalyst by passing hot gases containing oxygen therethrough, the method of preventing the formation of iron carbonyl by interaction of carbon monoxide formed in the regeneration with the iron of the steel alloy which comprises constructing those portions of the apparatus exposed to the'hot gases during regeneration of steel containing from 24 to 26% chromium, 19 to 21% nickel, between 0.2 and 2% of silver and the balance iron and small amounts of carbon and other elements which do not interfere with the effect of the silver on the steel.

2. In catalytic reforming in the presence of hydrogen carried out in apparatus constructed of or lined with the 25 chromium-20 nickel type of stainless steel and in the presence of a catalyst which requires periodic regeneration to restore its activity, said regeneration being eifected by burning on? the coke deposited on the catalyst by passing hot inert-gases contaming oxygen therethrough at a temperature between 650 and 1200 F., the method of preventing the formation of iron carbonyl by interaction or the carbon monoxide evolved in the regeneration with the iron in the steel alloy which comprises constructing those portions of the apparatus exposed to the hot gases during regeneration of steel containing from 24 to 26% chromium, 19 to 21% nickel, 0.2 to 1.8% silver and the balance iron and small .amounts of carbon and other impurities which do notinterfere with the effect of the silver on the steel.

' ROBERT P. RUSSELL. 

